1. Field of the Invention
The present invention relates to a semiconductor device, particularly, a semiconductor device utilizing trench isolation.
2. Description of the Related Art
Trench isolation is utilized in many cases in the field of semiconductor devices. For example, trench isolation is utilized for isolating metal oxide semiconductor (MOS) transistors or bipolar transistors.
In trench isolation technique, a trench (or groove) is formed by a selective etching method in a semiconductor substrate such as a silicon substrate, followed by filling the trench with an insulating material such as silicon oxide. For example, a mask material layer such as a silicon nitride layer or a silicon oxide layer is formed first on a semiconductor substrate, followed by patterning the mask material layer. Next, a surface region of the semiconductor substrate is etched by using the patterned mask material layer as an etching mask so as to form a trench in the semiconductor substrate. Then, an insulating material layer such as a silicon oxide layer is formed on the semiconductor substrate by, for example, a chemical vapor deposition (CVD) method or a solution coating method so as to bury the insulating material in the trench. Further, the surface on the side of the insulating layer is planarized by, for example, a dry etching method or a chemical mechanical polishing (CMP) method, thereby forming an isolating region.
It should be noted that a gigantic trench is formed in some cases in a semiconductor device such as a power MOS field effect transistor (FET). For example, in some cases, a gigantic trench having a width in the range of 3 μm to 15 μm and a depth in the range of 20 μm to 70 μm is formed.
Where the trench is relatively small, an insulating material can be buried in the trench by, for example, a CVD method. However, it is difficult to employ a CVD method for burying an insulating material in a gigantic trench.
In a solution coating method, the surface of a semiconductor substrate is coated, for example, by a spin coating method with a solution prepared by dissolving silanol etc. in an organic solvent, i.e., Spin On Glass (SOG), followed by baking the coating film so as to bury an SOG layer in the trench. The solution coating method is suitable for burying an insulating material in a larger trench, compared with the CVD method. However, SOG is low in viscosity, and it is necessary to repeat the coating treatment many times for forming an insulating layer buried in a gigantic trench. Also, even if the gigantic trench can be filled with the SOG layer, a problem tends to be arise in that a defect such as cracking occurs in the SOG layer when heat treatment such as an activating annealing treatment is performed.
It is disclosed in U.S. Pat. No. 4,544,576 that a trench formed in a silicon substrate is filled with a suspension containing glass particles, followed by applying heat treatment at a temperature high enough to fuse the glass particles so as to form a continuous glass layer. This method is considered to make it possible to fill a gigantic trench with an insulating material. However, in order to suppress the occurrence of defects in this method, it is necessary to use glass having a thermal expansion coefficient substantially equal to that of the silicon substrate. In other words, it is difficult to select the material used for forming the isolating region in view of, for example, the insulating properties.